'88 T2 sat for 3 years but in large garage. No moisture. Over that time did a number
of things, complete a/c rebuild, water pump, calipers etc. Nothing electrical.
Now when I drive left turn signal flashes very fast. All bulbs new & working.
Have checked connections Is it the switch or ??? Help, please

 

Most likely it's your turn signal flasher (https://www.atkinsrotary.com/86-92-R...01-67-564.html). After sitting for a long time without use, the electrolytic capacitors on that board will dry out and no longer function. If you're handy with a soldering iron and want to save a few $$, than you might want to try replacing the capacitors yourself and see if that fixes your problem.